NL-25-0390, Proposed Inservice Inspection Alternative FNP-ISI-ALT-2025-10 for Containment Unbonded Post-Tensioning System Inservice Inspection Requirements in Accordance with 10 CFR 50.55a(z)(1) Response to Request for Additional Info
| ML25282A075 | |
| Person / Time | |
|---|---|
| Site: | Farley  |
| Issue date: | 10/09/2025 |
| From: | Coleman J Southern Nuclear Operating Co |
| To: | Office of Nuclear Reactor Regulation, Document Control Desk |
| References | |
| NL-25-0390, FNP-ISI-ALT-2025-10 | |
| Download: ML25282A075 (1) | |
Text
Regulatory Affairs 3535 Colonnade Parkway Birmingham AL 35243 205 992 5000 October 9, 2025 Docket Nos.: 50-348 NL-25-0390 50-364 U. S. Nuclear Regulatory Commission ATTN: Document Control Desk Washington, D. C. 20555-0001 Joseph M. Farley Nuclear Plant, Units 1 and 2 Proposed Inservice Inspection Alternative FNP-ISI-ALT-2025-10 for Containment Unbonded Post-Tensioning System Inservice Inspection Requirements in Accordance with 10 CFR 50.55a(z)(1)
Response to Request for Additional Information Ladies and Gentlemen:
By letter dated February 27, 2025 (Agencywide Documents Access and Management System (ADAMS) Accession No. ML25058A186), Southern Nuclear Operating Company (SNC) submitted a proposed alternative, Alternative FNP-ISI-ALT-2025-10. The proposed alternative would extend the inspection exam frequency of ASME Section XI Table IWL-2500-1 Examination Category L-B for item numbers L2.10, L2.20, L2.30, L2.40 and L2.50.
By email dated September 9, 2025, the U.S. Nuclear Regulatory Commission (NRC) staff provided a request for additional information (RAI) as discussed in the Enclosure to this letter.
The RAI response is documented in the Enclosure.
This letter contains no NRC commitments. If you have any questions, please contact Ryan Joyce at 205.992.6468.
Respectfully submitted, Jamie M. Coleman Regulatory Affairs Director JMC/was/cbg Digitally signed by JAMIEMCO Date: 2025.10.09 14:37:45 -05'00'
U. S. Nuclear Regulatory Commission NL-25-0390 Page 2
Enclosure:
Response to Request for Additional Information cc:
Regional Administrator, Region ll NRR Project Manager - Farley Nuclear Plant Senior Resident Inspector - Farley Nuclear Plant RType: CFA04.054
ENCLOSURE Response to Request for Additional Information
Enclosure to NL-25-0390 Response to RAI 1
REQUEST FOR ADDITIONAL INFORMATION BY THE OFFICE OF NUCLEAR REACTOR REGULATION FARLEY UNITS 1 AND 2 - ISI ALTERNATIVE FOR TENDON ISI EXTENSION SOUTHERN NUCLEAR OPERATING COMPANY FARLEY, UNITS 1, 2 DOCKET NO. 05000348, 05000364 ISSUE DATE: September 9, 2025 Question 1 Regulatory Basis:
ASME BPV Code,Section XI, IWL-2421(b) states, for sites with multiple plants utilizing the same prestressing system and are essentially identical in design, the inspection dates and examination requirements may be as follows.
For the containment with the first Structural Integrity Test, all examinations required by IWL-2520 shall be performed at 1, 3, and 10 years and every 10 years thereafter. In addition, the examinations required by IWL-2524 and IWL-2525 shall be performed at 5 and 15 years and every 10 years thereafter.
For each subsequent containment constructed at the site, all examinations required by IWL-2520 shall be performed at 1, 5, and 15 years and every 10 years thereafter. In addition, the examinations required by IWL-2524 and IWL-2525 shall be performed at 3 and 10 years and every 10 years thereafter.
Background:
Section 5.0 of the enclosure to the proposed alternative FNP-ISI-ALT-2025-10 proposes the following alternative to IWL-2421(b) examination schedules:
For both Units 1 and 2, tendon force measurements required by Table IWL-2500-1 Examination Category L-B, item number L2.10 shall be performed in 2031 and every 20 years thereafter: the examination to be performed in 2026 in accordance with the current schedule would be skipped.
For both Units 1 and 2, examination of tendon anchorage areas, corrosion protection medium, and free water required by Table IWL-2500-1 Examination Category L-B, item numbers L2.30, L2.40, and L2.50 shall be performed in 2031 and every 10 years thereafter: the examinations to be performed in 2026 in accordance with the current schedule would be skipped.
Issues:
The proposed alternative includes future alternatives to IWL-2421(b) for the year 2026 (50th year for Unit 1 and 45th year for Unit 2) and beyond. However, the alternatives for 2041 and beyond fall outside the current period of extended operation for Unit 1, for which the renewed facility operating license expires on June 25, 2037, and are thus not within the review scope. Similarly, the alternatives for 2046 and beyond fall outside the current period of extended operation for Unit 2, for which the renewed facility operating license expires on March 31, 2041, and are thus also not within the review scope. The proposed alternative for 2041 and beyond for Unit 1 and for 2046 and beyond for Unit 2 is outside the current licensing period, and NRC cannot authorize an alternative beyond the current end of the license.
Enclosure to NL-25-0390 Response to RAI 2
Request:
Clarify the proposed alternative to address the containment ISI schedule within the scope of authority granted by the renewed facility operating licenses and associated license expiration dates.
SNC Response to RAI - Question 1 The Farley Unit 1 operating license is set to expire June 25, 2037, and the Farley Unit 2 operating license is set to expire March 31, 2041. This alternative request is to perform examinations on an extended frequency. The examination schedule provided in Table 2 of Section 5.0, Proposed Alternative and Basis for Use, currently goes beyond the current life of plant to match the evaluation to extend the frequency of exams. Since examinations on both units are scheduled together, this alternative will expire with the expiration of the Unit 1 License on June 25, 2037. The schedules of IWL examinations will default back to the ASME Section XI Code requirements, unless a subsequent alternative is authorized by the NRC. Please see the table below for the updated schedule.
Proposed Tendon Surveillance Schedule (includes the four most recent Unit 1 and Unit 2 surveillances for reference)
Year Units 1 & 2 Visual Examination, CPM Sampling &
Free Water Collection / Testing Tendon Force Measurement 2006 Performed Performed 2012 Performed N/A 2017 Performed Performed 2021 Performed N/A 2031a Perform Perform Note a: For scheduling purposes, each future surveillance is due at mid-year and must be performed between 30 June of the year prior to the year shown and 30 June of the year following the year shown.
Question 2 Regulatory Basis:
ASME BPV Code,Section XI, IWL-2421(b) states, for sites with multiple plants utilizing the same prestressing system and are essentially identical in design, the inspection dates and examination requirements may be as follows.
For the containment with the first Structural Integrity Test, all examinations required by IWL-2520 shall be performed at 1, 3, and 10 years and every 10 years thereafter. In addition, the examinations required by IWL-2524 and IWL-2525 shall be performed at 5 and 15 years and every 10 years thereafter.
For each subsequent containment constructed at the site, all examinations required by IWL-2520 shall be performed at 1, 5, and 15 years and every 10 years thereafter. In addition, the examinations required by IWL-2524 and IWL-2525 shall be performed at 3 and 10 years and every 10 years thereafter.
Enclosure to NL-25-0390 Response to RAI 3
Background:
- 1. Section 5.0 of the proposed alternative FNP-ISI-ALT-2025-10 enclosure proposes the following alternative to IWL-2421(b) examination schedules:
For both Units 1 and 2, examination of tendon anchorage areas required by Table IWL-2500-1 Examination Category L-B, item numbers L2.30 shall be performed in 2031 and every 10 years thereafter: the examinations to be performed in 2026 in accordance with the current schedule would be skipped.
- 2. The corrective actions performed after the 2012 failure of the Unit 1 hoop tendon H7AB field end anchor head included:
Replacing Unit 1 tendon H7AB Replacing the field anchor heads on the following tendons found to have low base number CPM:
Unit 1: H13AC, H25AC, H27AC, H29AB, H33AB, H35AB, H41AB and D322 Unit 2: H5DE, V60, D220 and D231 Issues:
The proposed alternative requests to extend the interval for the examination of tendon anchorage areas, as specified in Table IWL-2500-1, Examination Category L-B, Item No. L2.30, from 5 years to 10 years. However, the NRC staff notes a history of unacceptable results related to this inspection item, specifically the failed or cracked tendon anchor heads discovered in 1985, 2012, and 2017. Code Case N-926, which outlines alternative examination requirements for unbonded post-tensioning systems of Class CC components, allows for extending inspection intervals if acceptance standards have been met or examination results have been accepted by engineering evaluation during the last three examinations. Although RG 1.147 does not formally endorse Code Case N-926, the staff considers the minimum requirement of three consecutive successful examinations to extend the interval to be reasonable. While no unacceptable observations were reported during the most recent inspection in 2021, the licensee does not appear to meet this criterion because anchor head failures or cracks were identified in the two prior inspections, in 2012 and 2017 -- in other words, two of the last three inspections revealed failures or cracks.
Request:
- 3. Clarify whether corrosion protection medium analysis in 2012 per Table IWL-2525-1, associated with Table IWL-2500-1 (L-B), Item No. L2.40, was performed on all containment tendon anchorage areas to determine the low-base number attributed to hydrogen stress cracking assumed to impact the thirteen replaced anchor heads.
- 4. Provide additional justification to demonstrate that the cracking mechanisms identified in the inspected anchor heads associated with Table IWL-2500-1 (LB), Item No. L2.30 inspections do not apply to the remaining uninspected anchor heads to ensure that they are not susceptible to similar cracking.
SNC Response to RAI - Question 2:
- 3. The original thirteen anchor heads picked to be replaced after the 2011 failures were based on prior IWL inspections. The anchor heads selected for replacement had grease with lower base numbers similar to failed anchor head H7AB. During the replacement activities it was determined that one of these anchor heads could not be replaced. There was another project at the same time where a device was used to get small samples of grease to test. A total of 501 samples were taken and compared to the grease characteristics of H7AB that had failed. Three additional tendons were chosen to replace the field end anchor head where the grease had some characteristics extremely similar to H7AB. No additional grease testing was done at the
Enclosure to NL-25-0390 Response to RAI 4
time of anchor head replacement since the small samples taken had been correlated to large volume samples. All the anchor heads removed were then subjected to magnetic particle testing and no cracking was found.
- 4. Attachment 1 to FNP-ISI-ALT-2025-10, section 4.2.4.3 (2017 event) discusses the failure of the field end anchor heads for H7AB (2011) and H11AB (2017), both from heat treatment lot 10114, and the removal of other anchor heads from this lot. Testing of all other anchor heads removed after the H7AB anchor head failure in 2011 and H11AB anchor head failure in 2017 from other heat treatment lots showed that none exceeded the allowable Rockwell Hardness (ref. 6.32 in Attachment 1 Extension Technical Report of proposed alternative FNP-ISI-ALT-2025-10). Therefore, it is concluded that with the removal of all anchor heads from heat treatment lot 10114 (which exceeded the allowable Rockwell Hardness in subsequent testing) that the issue of any future anchor heads cracking has been addressed.
Question 3 Regulatory Basis:
ASME BPV Code,Section XI, IWL-2521(d) and IWL-2521.2(a) state the followings regarding the relation between the tendons to be inspected per the augmented examination requirements following repair/replacement activities (Table IWL-2521-2) and the tendons to be inspected per general (i.e., non-augmented) examination requirements (Table IWL-2521-1).
2521(d): The population of tendons from which a random sample is drawn for examination in accordance with Table IWL-2521-1 need not include tendons subject to augmented examination in accordance with Table IWL-2521-2.
2521.2(a): Tendons requiring augmented examination in accordance with Table IWL-2521-2 shall be randomly selected from the population of tendons affected by a repair/replacement activity.
In addition, regarding augmented examinations, ASME BPV Code,Section XI, Table IWL-2521-2 requires that, after the initial inspection (1 year following completion of the repair/replacement activity), subsequent inservice inspections scheduled to coincide with IWL-2420 following completion of the repair/replacement activity be performed, where the required minimum number of affected tendons of each type to be examined may be reduced to the lesser of 2% or 5 tendons, if the acceptance criteria of IWL-3221.1 have been met for the last 2 (two) inspections.
Background:
Section 5.0 of the proposed alternative FNP-ISI-ALT-2025-10 enclosure proposes the following alternative to IWL-2521(d) and IWL-2521.2(a) for augmented examination samples:
Include Unit 1, Groups 1 and 2 (tendons repaired/replaced in 2012 and 2017, respectively) in Population 1 (all tendons not previously in a surveillance sample or in Groups 1 and 2).
Issues:
The licensees proposal to include Unit 1, Groups 1 and 2 in Population 1 would effectively eliminate the augmented examinations required by IWL 2521.2(a), reducing the number of tendons to be examined, and consequently, reducing the number of anchorage areas examined under Table IWL-2500-1, Examination Category L-B, Item No. L2.30. Table IWL-2521-2
Enclosure to NL-25-0390 Response to RAI 5
provides the framework for the minimum requirement of two consecutive successful examinations to reduce the required minimum number of affected tendons to be examined in augmented examinations. Even though no unacceptable results were found during the most recent inspection in 2021, the licensee does not appear to meet this criterion because anchor head failures or cracks were identified in the prior inspection in 2017. In other words, one of the last two inspections revealed failures or cracks. Additionally, due to a history of unacceptable results related to this inspection item, specifically failed or cracked tendon anchor heads discovered during prior inspections in 1985 and 2012, the NRC staff questions whether there is reasonable assurance that other cracked anchor heads would not exist since the recent inspections that were based on a small random sample size and discovered numerous cracked anchor heads.
Request:
Provide additional documentation to demonstrate an acceptable level of quality and safety when Groups 1 and 2 are included in Population 1 for random tendon sampling (i.e., inspection results of Groups 1 and 2 augmented inspections have been acceptable for the last two consecutive examination periods per Table IWL-2521-2).
SNC Response to RAI - Question 3:
Farley Nuclear Plant Relief Request Technical Report Rev. 1 Ref. 6.22 and 6.23 (Attachment 1 Extension Technical Report of proposed alternative FNP-ISI-ALT-2025-10) contain the inspection results for Augmented Group 1 and 2. Augmented Group 1 included lift-off for one tendon in 2017 then visual only inspection for a different tendon in 2021. Group 2 included visual only inspection for one tendon in 2021. The second examination of Group 2 has not been completed. However, after the analysis of the failed anchor heads in 2017, a replacement project of all anchor heads from lot 10114 was completed. These replacements removed all anchor heads from tendons that have failed previously and any anchor heads from the lot 10114. SNC will perform the Group 2 second consecutive exam consistent with code requirements in 2031 during the scheduled inspection. All IWL code acceptance criteria were met during the previous required inspections (Ref. 6.22 and 6.23 in Attachment 1 Extension Technical Report of proposed alternative FNP-ISI-ALT-2025-10).
Additionally, see question 2 above that discusses the removal of all anchor heads from heat treatment lot 10114 where the issue of high Rockwell hardness contributed to the cracking.
All other anchor heads that were removed from other lots had Rockwell hardness in the acceptable range. The failures in 2011 and 2017 were anchor heads from the same lot 10114 and previously removed anchor heads from that same lot had high Rockwell hardness. No other heat treatment lots have been outside the acceptable range; therefore, it is concluded the issue with any potential anchor head cracking has been addressed.